NCIt definition : A synthetic ethanolamine, with anticholinergic, sedative, and histamine H1 antagonistic
activities. Upon administration, clemastine blocks the H1 histamine receptor and prevents
the symptoms that are caused by histamine activity on capillaries, bronchial and gastrointestinal
smooth muscles, including vasodilation, increased capillary permeability, bronchoconstriction,
and spasmodic contraction of gastrointestinal smooth muscles. Clemastine also prevents
histamine-induced pain and itching of mucous membranes.;